Add website to client repository

Closes #1567

The main reason I'm not simply merging Annika's PR is because this
way makes it clearer that I'm taking responsibility for all this
code, that it's mostly code I wrote, and also because it makes it
easier to ensure that none of the files have been changed.

(Not that I don't personally trust Annika, but I have something
resembling an obligation to users not to expose them to risks based
on personal trust.)

website/lib/htmlpurifier/HTMLPurifier/ConfigSchema/Interchange/Id.php

@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * Represents a directive ID in the interchange format.
+ */
+class HTMLPurifier_ConfigSchema_Interchange_Id
+{
+
+    public $key;
+
+    public function __construct($key) {
+        $this->key = $key;
+    }
+
+    /**
+     * @warning This is NOT magic, to ensure that people don't abuse SPL and
+     *          cause problems for PHP 5.0 support.
+     */
+    public function toString() {
+        return $this->key;
+    }
+
+    public function getRootNamespace() {
+        return substr($this->key, 0, strpos($this->key, "."));
+    }
+
+    public function getDirective() {
+        return substr($this->key, strpos($this->key, ".") + 1);
+    }
+
+    public static function make($id) {
+        return new HTMLPurifier_ConfigSchema_Interchange_Id($id);
+    }
+
+}
+
+// vim: et sw=4 sts=4